Chapter 16 the Israelites despite all that God has done for them already, start complaining that they will starve to death. They still don't fully trust God. If they had they could have inquired instead of grumbling to the Lord about their food situation. How often are we the same way? God does all these things for us yet, when the next problem/issue arrises we start grumbling about it. Thankfully we all have a loving and caring God that provides for us and will never leave or forsake us.
Verse 16:18 "...whoever gathered much had nothing left over, and whoever gathered little had no lack..." God provides for our needs. Paul quotes this verse in 2 Corinthians 8:15 encouraging giving generously so all needs are met. If they had an abundance that could help those that were lacking otherwise, then why not help instead of hoarding the good gifts God provided. It would in turn encourage those on the receiving end to do the same when they have the means to fulfill a need.
On the sixth day of the week they were told to gather twice as much so they would have a day of rest. It set a precedent for when they were out of the wilderness and had to do more labor. Our bodies and souls need rest to function properly. The sabbath is a day to let our physical bodies recover and our souls to get replenished.